Double oxidative addition reaction of dihalomethane to dinuclear

t-BuS)(CO)(P(OMe)3]2[.mu.-CH2] .... (M = Rh, Ir) with Alkyl Halides: Dramatic Reactivity Differences as a Function of Metal Combination and Alkyl Hali...
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Organometallics 1985, 4, 773-780

Double Oxidative Addition Reaction of Dihalomethane to Dinuclear Iridium( I)Complexes: Preparation and Properties of Some Methylene-Bridged Diiridium( II I)Complexes. X-ray Structure of [ Ir I(p-f -BUS)(CO) (P( OMe)&[ p-CH2] Mohamed El Amane, Andre Maisonnat, FranGoise Dahan, Robert Pince, and Ren6 Poilblanc" Laboratoire de Chimie de Coordination du CNRS associ6 B I'Unlversit6 Paul Sabatier, 3 1400 Toulouse, France Received August 2, 1984

Thiolato-bridged diiridium(1) complexes [Ir(r-t-BuS)(CO)L],, 1, react with dihalomethane to yield quantitatively [IrX(p-t-BuS)(CO)LI2[p-CH2], 2 (X = I, L = CO, P(OMe),, PPh,, PPh2Me, PMe,; X = Br, L = PPh,). Cis and trans isomers were observed in two cases. A crystal structure determination of [IrI(p-t-BuS)(CO)(P(OMe),],(p$H,] was carried out by X-ray diffraction. The compound crystallizes in orthorhombic space group D,-Pbca in a cell of dimensions a = 17.033 (3) A, b = 15.632 (2), and c = 23.808 (3) A, with 2 = 8. On the basis of 3106 unique reflections having F,2 > 4a(F:), the structure was refined by full-matrix least-squares technique to conventional agreement indices of R = 0.024 and R, = 0.027. Each iridium atom is octahedrally coordinated, being bound to one carbonyl, one phosphite, one iodide ligand, two bridging S atokns of the thiolato ligands, and the bridging C atom of the CH2 group. The phosphite ligands (and the carbonyl ligands) are in a trans arrangement. The t-Bu groups are in an anti conformation with respect to the Ir2Szcore. The IrIr separation is 3.1980 (4) A. In solution, complexes 2 undergo syn-anti isomerization on the NMR time scale. The halogen abstraction reaction of 2 by silver(1) salts and the subsequent addition of nucleophilic reagents to the cationic species so obtained are described together with the molecular structure of the products.

Introduction

A large number of p-alkylidene complexes has now been prepared and characterized.' If diazoalkanes remain probably the most versatile precursors for their direct synthesis,the geminal dihalogenoalkane route is of growing interest in their reactions h t h anionic dimetallic species.2 On the other hand, very few examples of their direct reaction with neutral organometallic substrates are known. To our knowledge, only two examples have been described so far that apply to t h e low oxidation s t a t e complexes Au~(CH~PM~~CH a n, d) , P~d , ( d ~ p m ) , . ~ Following our studies of the reactivity of thiolato-bridged homobimetallic species toward small molecule^,^ we present here t h e preparation of novel p-methylene complexes [I~X(~-~-BUS)(CO)L]~[~-CH,] (2) via quantitative double oxidative addition reactions of dihalomethane with diiridium( I) complexes [Ir ( p -t-BUS)(CO) L]2, 1. These p-methylene complexes afford cationic species through halogen abstraction. It is t h e vacant sites so obtained which make these electron-deficient species, whose reactivity is introduced in this paper, of particular interest.

Experimental Section General Remarks. All reactions and manipulations were routinely performed under a nitrogen or argon atmosphere in Schlenk-type glassware. All solvents were appropriately dried and freed from molecular oxygen prior to use. Microanalyses were performed by the Service Central d'Analyse du CNRS or by the Service de Microanalyses du Laboratoire de Chimie de Coordi(1)Hermann, W. A. Ado. Organomet. Chem. 1982, 20, 159-263. Holton, J.; Lappert, M. F.; Pearce, R.; Yarrow, P. I. W. Chem. Reo. 1983, 83,135-201. (2)Sumner, C. E.,Jr.; Riley, P. E.; Davis, R. E.; Pettit, R. J. Am. Chem. SOC.1980,102,1752-1754. Theopold, K. H.;Bergman, R. G. J. Am. Chem. SOC.1983,105, 464-475. (3)Jandik, P.; Schubert, U.; Schmidbaur, H. Angew. Chem., Int. Ed. Engl. 1982,21,73;Angew. Chem. Suppl. 1982,1-12. (4) Balch, A. L.; Hunt, C. T.; Lee, C. L.; Olmstead, M. M.; Farr, J. P. J. Am. Chem. SOC.1981,103, 3764-3772. (5)Poilblanc, R. Inorg. Chim. Acta 1982,62,75-86.

0276-7333/85/2304-0773$01.50/0

nation du CNRS. Mass spectra were recorded on a Varian MAT 311 A. Conductivity data were determined for lo-, equivl-' solutions in methanol with a commercial conductivity bridge instrument. Infrared spectra were recorded in hexane or dichloromethane solutions, using a Perkin-Elmer Model 225 grating spectrometer; in the carbonyl stretching region, the spectra were calibrated with water vapor lines. lH NMR spectra were obtained at 90 and/or 250 MHz on a Bruker WH 90 PT and/or a Bruker WM 250 FT spectrometer. Chemical shifts were measured with respect of internal tetramethylsilane and are given in parts per million downfield positive. 31PNMR spectra were measured at 36.4 MHz on a Bruker WH 90 FT spectrometer; chemical shifts were measured with respect to external H3P04and are given in parts per million downfield positive. 13CNMR spectra were recorded at 62.9 MHz on a Bruker WM 250 FT spectrometer; chemical shifts were measured with respect to internal tetramethylsilane and are given in parts per million downfield positive. Preparation of Compounds. The starting materials [Ir(p~ - B U S ) ( C O ) ~la: ] ~ ,and [Ir(p-t-BuS)(CO)(PR,)],, lb-e,' were prepared according to published procedures. Preparation of [I~I(~-~-BUS)(CO)~]~[~-CH~], 2a. Diiodomethane (0.5 mL) wm added to a solution of [Ir(p-t-B~S)(C0)~1, (0.300mg, 0.444 mmol) in hexane (20 mL). A yellow precipitate. appeared. After 1 h, the product was filtered off, washed with hexane, and dried in vacuo. The IR spectrum of the filtrate indicated the total consumption of the starting material and the formation of only one product. The product was recrystallized from methanol; electron-impact MS (70 eV), m / e 944 (M') plus fragment ions corresponding to successive loss of four CO groups and two I atoms. Anal. Calcd for C13H2012Sz041rz: C, 16.56; H, 2.14. Found: C, 16.55; H, 2.14. Preparation of [IrI(p-t -BUS)(CO)(P(OM~),)]~[~-CH?], 2b. Diiodomethane (0.05 mL, 0.63 mmol) was added to a solution of [~GL-t-BUS)(CO)P(OMe)3]z (0.25 g, 0.29 "01) in hexane (15 mL). The solution changed within a few minutes from orange to pale ~

~~

(6) de Montauzon, D.; Poilblanc, R. Inorg. Synth. 1980,20,237-240. (7)de Montauzon, D.; Kalck, P.; Poilblanc, R. J. Organomet. Chem.

1980,186,121-130. (8)Bonnet, J.-J.; Kalck, P.; Poilblanc, R. Angew. Chem.,Int. Ed. Engl. 1980, 19, 551-552. Kalck, P.; Bonnet, J.-J. Organometallics 1982, I, 1211-1216.

0 1985 American Chemical Society

774 Organometallics, Vol. 4,No. 4, 1985

El Amane et al.

Q-'-cm2.mol-'. Anal. Calcd for C4BH50C1202P2S21r2: C, 41.67; H, yellow, and a pale yellow precipitate slowly appeared. The 3.57. Found: C, 41.11; H, 3.28. precipitate was filtered, washed with petroleum ether, and dried 6a may also be prepared by the simultaneous action of AgClO, under vacuum (0.24 g, 73%). Anal. Calcd for C17HB12S208P21r2: and PPh, on a solution of 2a in dichloromethane. Monitored by C, 17.99; H, 3.38. Found: C, 18.32; H, 3.50. IR over a period of 6 h, the spectra indicated the slow formation White and yellow crystals were obtained by fractional crysof 6a together with the formation and the disappearance of a tallization on cooling methanol solutions of the pale yellow premonocationic intermediate, 5a, having three u(C0) bands at 2115, cipitate at -20 "C. The two products correspond to two isomers 2105, and 2067 cm-'. of the title compound, 01 and /3, as demonstrated by the X-ray Preparation of ([I~(~-~-BUS)(CO)~(P(OM~)~)]~ structure determination of the white crystals together with NMR CH2])2+(C10,)2, 6b, and IR Characterization of ([Ir(p-tstudies of both compounds. BUS)(CO) (P(OMe)3)]2[p-CH2])2+(C10~)2, 4b, and [ (CO)(PPreparation of [I~I(~-~-BUS)(CO)(PP~~)]~[~-CH~], 2c. (OMe)3)IIr(p-t-BuS)2(p-CH2)Ir(P(OMe)3)(CO)~]~ClO4~, 5b. Diiodomethane (0.15 mL, 1.86 mmol) was added to an orangeA solution of the white a isomer of 2b (0.305 g, 0.27 mmol) in (1.065 g, 0.93 mmol) yellow solution of [Ir(y-t-BuS)(C0)(PPh,)l2 dichloromethane (20 mL) was allowed to react with AgC10, (0.115 in dichloromethane (15 mL). The u(C0) region of the IR spectrum g, 0.55 mmol) a t room temperature. After 2 h, the initial comof the solution indicated totd consumption of the starting material pound 2b was consumed and the IR spectrum indicated the within a few minutes. The resulting pale yellow solution was presence of a new compound, 4b, having a single broad v(C0) band concentrated under vacuum. Hexane was added dropwise to at 2069 cm-'. The solution was filtered, and the filtrate then was precipitate a pale yellow solid. After the mother liquor was allowed to react with carbon monoxide at room temperature and decanted, the solid was washed with hexane and dried under atmospheric pressure. The changes in the IR spectrum indicated vacuum (1.089 g, 83%). The product may be recrystallized from dichloromethane-methanol. Anal. Calcd for C47H5012S202P21r2: the formation of a new complex, 6b, having three v(C0) bands at 2112,2080, and 2065 cm-', after a reaction time of 30 min. The C, 40.00; H, 3.58; I, 17.98; S, 4.54. Found: C, 39.95; H, 3.57; I, solution was concentrated under reduced pressure and methanol 17.80; S, 3.74. was added. Preparation of [IrBr(p-t-BUS)(CO)(PPh3)12[p-CH21,2f. Crystallization at -20 "C gave pale yellow crystals of 6b (0.191 This complex was prepared from dibromomethane and [Ir(p-tg, 62%): conductivity, A = 225 Q-'.cm2.mol-'. Anal. Calcd for BuS)(CO)(PPh,)], by the method used for the preparation of 2c. C19HBC1201sP2S21rz: C, 20.09; H, 3.37. Found: C, 19,87;H, 3.84. The reaction time was much longer, and the IR spectrum of the 6b may also be prepared by the simultaneous action of silver solution indicated the total transformation of the starting material perchlorate and carbon monoxide on a solution of 2b in diinto the title compound after 25 h. chloromethane. Under these conditions, the intermediate 5b, Preparation of [IrI(p-t-BuS)(CO)(PPh2Me)12[p-CH21, 2d. having v(C0) bands at 2115,2070, and 2055 cm-', was detected. This complex was prepared by the procedure used for 2c, in Preparation of ([I~(~-~-BuS)(CO)(P(OM~)~)~~~[~hexane solution. Anal. Calcd for C37H&S202P2Ir2: c , 34.53; (C104-)26b'. A solution of 2b (0.250 g, 0.22 mmol) in dichloroH, 3.61; I, 19.72; S, 4.98. Found: C, 34.53; H, 3.54; I, 20.02; S, methane (15 mL) was allowed to react simultaneously with AgClO, 4.75. (0.091 g, 0.44 mmol) and P(OMe)3(5 pL, 0.44 mmol). After 2 h, Preparation of [1rI(p-t-B~s)(Co)(PMe~)]~[p-CH~], 2e. As the initial compound 2b was consumed and the IR spectrum for 2b, addition of diiodomethane to an hexane solution of [Irindicated the presence of a new compound 6b' having two v(C0) (p-t-BuS)(C0)(PMe3)'J2 lead to the formation of a pale yellow bands at 2069 and 2059 cm-'. The solution was filtered, and the precipitate within a few minutes. Anal. Calcd for filtrate was concentrated under reduced pressure to about 7 mL. C1,HB12S202P21r2:C, 19.65; H, 3.69; I, 24.43; S, 6.17. Found: C, Methanol (7 mL) was added to the residue. Crystallization at 19.61; H, 3.73; I, 24.49; S, 5.62. -20 "C gave white crystals of 6b' (0.205 g, 70%): conductivity, Two kinds of crystals were obtained by fractional crystallization -1 = 219 n-'.cm2.mol-'. Anal. Calcd for C23HMC12022P,SzIrz: C, on cooling methanol solutions of the pale yellow precipitate, 20.80; H, 4.25. Found: C, 20.73; H, 4.06. corresponding to two isomers of the title compound. Preparation of ([Ir(p-t-BUS)(CO)~(PP~,)]~[~-CH J12+(PFg)2, Reaction of [IrI(p-t -BuS)(CO)(P(OMe),)12with Diazo6c. and IR Characterization of IrIr(u-t-BuSMCOMPPhd19., methane. [I~I(~-~-BuS)(CO)(P(OM~)~)]~ (0.2 mmol) prepared [pkH2]12:(PF6-)2, 4c. AgPF6 (0.182 g , 0.72 mmol) was according to the published method: placed in the outside tube to a solution of 2c (0.512 g, 0.36 mmol) in dichloromethane (15 of an Aldrich MNNG diazomethane kit, was allowed to react at mL) at room temperature. After 1h the initial compound 2c was 0 "C with diazomethane produced by 0.3 g (2.25 mmol) of N consumed and the IR spectrum indicated the presence of a new methyl-N'-nitro-N-nitrosoguanidineand 1.5 mL of 5 N sodium compound 4c having a v(C0) band a t 2034 cm-*. The solution hydroxide. No reaction was detected after 20 h, as indicated by was filtered, and the filtrate then was allowed to react with carbon the IR spectrum. monoxide at room temperature and atmospheric pressure. After Reaction of Complexes 2 with Silver(1) Salts. Preparation a reaction time of 15 min, the IR spectrum indicated the total of ([I~(~-~-BUS)(CO)~(PP~~)]~[~-CH,H~+(C~O~-)~, 6a, and IR of 4c into a new compound 6c having v(C0) bands Characterization of [(C0)211r(p-t - B u S ) ~ ( ~ - C H ~ ) I ~ ( C O ) ~conversion ~+and 2016 cm-'. The solution then was concentrated c104-,3a, ( [ I ~ ( ~ - ~ - B U S ) ( C O ) ~ ] ~ [ ~ - C H ~ ] 4a, ~ ~ +and [ C ~ O ~ at - ] 2081,2041, ~, [(CO)2IIr(p-t-BuS)2(~-BuS)2(~CH2)Ir(CO)2(PPh3)]tClO4-,under reduced pressure to half its volume, and methanol was added. Crystallization at -20 "C gave 6c as a yellow solid (0.295 5a. A solution of [IrI(p-t-B~s)(Co)~l~[p-CH~], 2a (0.200 g, 0.21 g, 54%): conductivity, A = 188 Q-'.cm2.mol-'. Anal. Calcd for mmol), in dichloromethane (15 mL) was allowed to react with C,gH,F1204P,S21r2: C, 39.15; H, 3.35. Found: C, 39.34; H, 3.33. AgC104(0.09 g, 0.43 mmol) in suspension at 0 "C. IR spectra were Crystal and Molecular Structure Determination of the periodically run over a period of 6 h. In the v(C0) region, the 01 Isomer of 2b. White parallelepipedic air-stable crystals were absorptions of the starting material 2a a t 2111, 2102, and 2062 obtained by slow cooling of a methanol solution of 2b to -20 "C. cm-' progressively decreased and two sets of new absorptions Preliminary film data on Weissenberg cameras indicated orthoappeared. A first set of absorptions at 2130,2115, and 2084 cm-', rhombic Laue symmetry. The observed systematic extinctions attributable to the intermediate monocationic species 3a, first lead to the Pbca space group. Data collection was carried out grew in and then disappeared. A second set of absorptions at 2143, on a CAD 4 Enraf-Nonius diffractometer. The final crystal pa2132, and 2098 cm-', attributable to the dication 4a, slowly grew rameters and the details of the data collection procedure are given in until the complete disappearance of the starting material 2a in Table I. and of the intermediate 3a. After 6 h, the spectrum exhibited Structure Solution and Refinement. The structure was the three bands of 4a, and later on no significant changes were solvedg by the heavy-atom technique. A Patterson map yielded observed. The solution was filtered and then triphenylphosphine positions for Ir and I atoms. Subsequent Fourier maps revealed (0.110 g, 0.42 mmol) was added to the filtrate at room temperature. the positions of all non-hydrogen atoms, which were refined anThe changes in the IR spectrum indicated the formation of a new complex, 6a, having three u(C0) bands a t 2104, 2093, and 2049 cm-'. The yellow solution was concentrated under reduced pressure, and petroleum ether was added. Crystallization at -20 (9) Sheldrick, G. M. 'Shelx 76", Program for Crystal Structure Determination; University of Cambridge: Cambridge, England, 1976. "C gave yellow crystals (0.240 g, 80%): conductivity, 12 = 193 I

1

Organometallics, Vol. 4, No. 4, 1985

Addition of Dihalomethane t o Dinuclear Iridium Complexes

775

Scheme I CH PX 2

[ I r (p-s- t - ~ u ) ( c O )LIP l a , L=CO b. L=P(OMe)3 c . LqPPh3 d, L=PPh2Me e. L=PMe3

-

[Ir X (,u

~

S - t-Bu)(CO)L] 21,~- CH 21

2a. L=CO. X.1 b. L=P(OMe)3, X = I LsFl'h3, X=I d. L=PPhzMe. X = I e, L=PMe3, X = I f. L=PPh3. X=Br t.

5a. L = CO. X = I. L' = PPh3, Y - = C104b. L = P(OMe13 X = I, L' = CO. Y- = ClQ-

Table I. Crystal Data and Experimental Details of the X-ray Diffraction Study of 2b Crystal Parameters a t 20 Oca formula c1?H381208p7.s21r2 fw 1134.81 cell parameters a, A 17.033 (3) b, A 15.632 (2) c , '4 23.808 (3) A3 6339.1 cryst system orthorhombic absences Okl, k = 2n + 1;h01,1= 2n t 1 ; hkO, h = 2n + 1 space group D&-Pbca

v,

z

a

d(calcd), g/cm3 2.378 d(obsd), g/cm3 2.25 (by flotation in 1,1,2,2tetrabromoethane/l,2-dichlorobenzene) F(000) 4208 Measurement of Intensity Data cryst dimens, m m 0.150 X 0.275 X 0.100 Mo KG from graphite radiation monochromatization receiving aperture 4.0 X 4.0 mm; 30 cm from crystal takeoff angle, deg 2.4 scan mode w-20 scan range, deg 0.70 + 0.35 tan 0 20 limits, deg 51 intensity std b 3 reflctns every 7200 s no. of independent 5686 reflectns collected Treatment of Intensity Data reductn to Fo2and corr for bkgds, attenuators and Lorentz-polarization '7(F02) in the usual manner linear abs coeff p , c m - * 105.5 absorption corrc Tmax= 0.374; Tmin = 0.162 obsd unique data 3106 (Fo2 2 4U(F0Z) no. of variables 298 R = IIFoI - lF,Il/x IFol 0.024 R, = ( Z W ( IFoI - lFCl)'/ 0.027 ZWF,~)'/~ W

P a From a least-squares fitting of the setting angles of 25 reflections. Showed only random, statistical fluctuations. Coppens, P. ; Leiserowitz, L. Rabinovitch, D. Acta Crystallogr. 1965, 18, 1035-1038. isotropically. The hydrogen atoms were localized on a ditterence Fourier map and introduced in the last cycles of refinement with constrained geometry (C-H= 0.95 A; H-C-H = 109.5') with an

Table 11. Final Least-Squares Atomic Coordinates with Estimated Standard Deviations for 2b x/a y/b 0.53778 (2) 0.27803 (2) 0.43050 ( 2 ) 0.20085 ( 2 ) 0.49560 ( 5 ) 0.36939 ( 5 ) 0.26713 ( 4 ) 0.20235 (5) 0.6172 (6) 0.3559 ( 7 ) 0.6616 (4) 0.4097 ( 5 ) 0.4222 ( 6 ) 0.0851 (8) 0.4136 ( 4 ) 0.0144 ( 5 ) 0.5493 ( 4 ) 0.2018 ( 6 ) 0.41500 (12) 0.20025 (14) 0.4092 (5) 0.0935 ( 6 ) 0.3303 (6) 0.0546 ( 7 ) 0.4044 (6) 0.1095 ( 7 ) 0.4752 (5) 0.0333 ( 6 ) 0.46355 (14) 0.34705 (15) 0.3841 ( 6 ) 0.4252 ( 6 ) 0.3272 ( 6 ) 0.3947 ( 7 ) 0.4278 ( 6 ) 0.5062 ( 6 ) 0.3432 ( 6 ) 0.4419 ( 7 ) 0.62418 (14) 0.20089 (18) 0.5908 ( 4 ) 0.1620 ( 4 ) 0.6332 ( 7 ) 0.1018 (8) 0.6607 (4) 0.1191 ( 4 ) 0.7177 ( 6 ) 0.1214 ( 7 ) 0.7025 ( 4 ) 0.2489 ( 5 ) 0.7126 (8) 0.3102 (8) 0.45785 (14) 0.22468 (17) 0.5461 ( 4 ) 0.2442 ( 4 ) 0.5993 ( 6 ) 0.1904 ( 9 ) 0.4153 (4) 0.3063 ( 4 ) 0.4301 (6) 0.3366 (8) 0.4423 ( 4 ) 0.1493 ( 4 ) 0.3673 ( 6 ) 0.1213 (a)

z/c 0.62689 (1) 0.52899 (1) 0.72389 ( 3 ) 0.51271 ( 3 ) 0.6128 ( 4 ) 0.6049 ( 3 ) 0.5142 ( 4 ) 0.5027 (3) 0.5548 (3) 0.63010 ( 9 ) 0.6642 ( 4 ) 0.6433 ( 4 ) 0.7266 (4) 0.6491 (4) 0.55123 (10) 0.5667 ( 5 ) 0.6114 ( 5 ) 0.5860 ( 4 ) 0.5112 ( 4 ) 0.67810 (11) 0.7341 ( 3 ) 0.7683 ( 4 ) 0.6491 ( 3 ) 0.6061 ( 5 ) 0.6950 ( 3 ) 0.7376 ( 6 ) 0.43780 (10) 0.4241 ( 3 ) 0.3994 ( 6 ) 0.4143 ( 3 ) 0.3582 ( 4 ) 0.3951 ( 3 ) 0.3772 ( 5 )

isotropic thermal parameter U = 0.06 A2. Neutral atom scattering factors for non-hydrogen atoms and corrections for anomalous dispersion effects for Ir, I, S, and P atoms were obtained from the tabulation of Cromer and Waber.lo Scattering factors for the hydrogen atoms were those of Stewart et al." The final cycle of refinement lead to R = 0.024 and R, = 0.027. The weighting scheme used in the minimization of the function x.w(lFol - lFc1)2is defined as w = 1/2(FO,+ (pFo)2where p is the factor to prevent overweighting of strong reflections. An analysis of variance according to F,,and (sin O ) / h showed satisfactory consistency. Atomic positional parameters with their (10)Cromer, D. T.; Waber, J. T. ''International Tables for X-ray Crystallography";Kynoch Press: Birmingham, England, 1974; Vol. IV, Table 2.2B, p 99. Cromer, D. T. Ibid. Table 2.3.1, p 149. (11)Stewart, R. F.; Davidson, E. R.; Simpson, W. T. J. Chem. Phys. 1965,42, 3175-3187.

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776 Organometallics, Vol. 4, No. 4, 1985

Table 111. Selected Interatomic Distances (A) with Esd’s for 2b

Figure 1. A perspective representation of [IrI(r-t-BuS)(CO)(P(OMe)3]2[p-CHz], 2b. The vibrational ellipsoids are drawn at the 40% probability level. Methylene hydrogens are drawn at an arbitrary scale. standard deviations are reported in Table 11.

Ir(1)-Ir(2) Ir( 1)-S( 1) Ir( 1)-S(2) Ir(1)-P(l) Ir( 1)-C( 1) Ir( 1)-I( 1) Ir(1)-C(17) P(1)-0(3) P(1)-0(4) P(1)-0(5) 0(3)-C(3) 0(4)-C(4) O( 5)-C(5) C(1)-0(1) S(l)-C(9) C(9)-C(lO) C(9)-C(ll) C(9)-C(12)

3.1980 ( 4 ) 2.420 (2) 2.451 (2) 2.260 (3) 1.850 (10) 2.8087 (8) 2.099 (8) 1.571 ( 7 ) 1.580(7) 1.583 ( 7 ) 1.438 (13) 1.413 (13) 1.404 ( 1 5 ) 1.147 (13) 1.858 ( 9 ) 1.557 (13) 1.509 (13) 1.510 (13)

Ir( 2)-S( 1) Ir( 2)-S( 2) Ir(2)-P(2) Ir( 2)-C( 2) Ir( 2)-I( 2) Ir(2)-C(17) P(2)-0(6) P(2)-0(7) P(2)-O(8) 0(6)-C(6) O( 7)-C( 7) O( 8)-C(8) C(2)-0(2) S(2)-C(13) C(13)-C(14) C(13)-C(15) C(13)-C(16)

2.422 (2) 2.412 ( 2 ) 2.251 ( 2 ) 1.848 (12) 2.8096 (8) 2.115 ( 7 ) 1.569 ( 7 ) 1.571 ( 7 ) 1.579 ( 7 ) 1.368 (14) 1.438 (12) 1.416 (12) 1.149 (14) 1.860 (10) 1.517 (15) 1.538 (14) 1.518 (15)

Table IV. Selected Bond Angles (deg) with Esd’s for 2b Results and Discussion S(l)-Ir(l)-S(2) 78.38 (8) S(l)-Ir(2)-S(2) 79.10 ( 8 ) The addition of diiodomethane to the complexes [Ir(pS(1)-Ir(1)-P(1) 106.12 (8) S(l)-Ir(2)-P(2) 169.02 (8) S(1)-Ir(1)-C(1) 165.4 ( 3 ) S(l)-Ir(2)-C(2) 100.2 ( 3 ) t-BUS)(CO)L],, la-e, in stoichiometric quantities as well 91.67 ( 5 ) S( 1)-Ir( 1)-I( 1) 90.48 ( 5 ) S( 1)-Ir( 2)-I( 2) as in large excess, in dichloromethane or hexane solution S(I)-Ir(l)-C(17) 79.7 ( 2 ) S(l)-Ir(2)-C(l7) 79.4 (2) at room temperature lead readily and quantitatively to S(2)-Ir(l)-P(l) 165.32 ( 9 ) S(2)-Ir(2)-P(2) 90.38 ( 9 ) (p-methylene)diiridium(III) (1/1) adducts [IrI(p-tS(2)-Ir(l)-C(l) 87.4 ( 3 ) S(2)-Ir(2)-C(2) 170.7 (3) BuS)(CO)L],[p-CH2],2a-e (Scheme I). No intermediates S(2)-1r(l)-I(l) 104.39 ( 6 ) S(2)-1r(2)-1(2) 104.68 ( 6 ) or byproducts were detected in solution. During the reS(2)-Ir(l)-C(l7) 72.4 (2) S(2)-Ir(2)-C(l7) 72.9 ( 2 ) P(1)-Ir(1)-C(1) 88.5 ( 3 ) P(2)-Ir(2)-C(2) 89.6 (3) action times, no reactions between the starting diiridium(1) 94.04 ( 6 ) P( 1)-Ir( 1)-I( 1) 89.67 ( 7 ) P( 2)-Ir( 2)-I( 2) materials and dichloromethane were observed. DiP(l)-Ir(l)-C(l7) 94.4 ( 2 ) P(2)-Ir(2)-C(l7) 94.6 (2) bromomethane reacts much more slowly and a bromo 90.1 ( 3 ) C(2)-Ir( 2)-I( 2) 84.6 ( 3 ) C( 1)-Ir( 1)-I( 1) analogue adduct, 2f, was obtained in the case where L = C(l)-Ir(l)-C(l7) 99.0 ( 4 ) C(2)-Ir(2)-C(l7) 97:8 (4) PPh3 after a reaction time of 25 h. I(l)-Ir(l)-C(17) 170.1 ( 2 ) 1(2)-1r(2)-C(17) 171.0 ( 2 ) Contrasting with the addition of CHJ, to la,c,d, which 82.22 ( 7 ) Ir(l)-S(l)-Ir(2) 82.67 ( 7 ) Ir(l)-S(2)-Ir(2) Ir(l)-S(l)-C(9) 120.7 (3) Ir(l)-S(2)-C(l3) 121.2 ( 3 ) gives 1/1 single adducts, the addition of CHz12to lb,e Ir(2)-S(l)-C(9) 116.3 ( 3 ) Ir(2)-S(2)-C(l3) 119.7 ( 3 ) yields a mixture of two isomeric adducts, a and @. MonIr( 1)-C( 17)-Ir(2) 98.7 ( 3 ) itored by proton NMR, the addition of CHzIz to l b in Ir(1)-C(1)-O(1) 174.0 ( 9 ) Ir(2)-C(2)-0(2) 176.0 (8) equimolar quantities leads to a mixture of the a and p isomers in the ratio [a]:[@]= 1:2. The relative concenPart of the molecule recalls the thiolato-bridged diiridium entity found in the starting material [Ir(p-ttration of a and /3 isomers in solution is remarkably stable BUS)(CO)(P(OMe)&]2,12 and the methylene group coming and the [a]:[@]ratio remains unchanged even after several from the added diiodomethane occupies a bridging position weeks. Pure a isomer was obtained by fractional crysbetween the iridium atoms. The iodide ligands, one on tallization as white parallelepipedic crystals. We did not each iridium in a terminal mode, are mutually trans to the succeed in preparing the pure @ isomer, and the correbridging methylene. Each iridium atom lies in a distorted sponding solid produds of fractional crystallizations always contained traces of the a isomer. No conversion of one octahedral environment, both octahedra sharing the face isomer into the other occurred, even upon heating for hours [S(l),S(2),C(l7)]. The tert-butyl groups of the thiolato bridging ligands are in an anti conformation with respect in refluxing hexane. to the IrzSzcore, whereas the carbonyl ligands and the These adducts form air-stable, pale yellow or white solids phosphite ligands occupy positions which confer a trans which dissolve readily in dichloromethane and tetraconformation to the molecule. I(1) and I(2) atoms are hydrofuran, to a lesser extent in toluene or methanol and slightly out of the plane [Ir(l),Ir(2),C(l7)]. They are 0.2172 are slightly soluble in petroleum ether. The structure of these new compounds has been resolved by an X-ray (8)and 0.2162 (8)A away from this plane, respectively, and are located on the same side. This is probably due to the diffraction analysis (in the case of Zb), elemental analyses, proximity of the bulky tert-butyl group around the C(13) a mass spectrum (in the case of 2a), IR spectra, and lH, 13C,and 31PNMR studies at room temperature and at low atom which is in exo position and which is located on the temperature. They correspond to double oxidative adother side of the plane [Ir(l),Ir(2),C(l7)].The 1r-h disdition of dihalomethane to the diirium(1) complexes. They tance is 3.1980 (4) A, and the dihedral angle between the may also be regarded formally as carbene adducts of the two planes containing [Ir(1),S(1),S(2)] and [Ir (2),S(l),S(2)] is 117.0’. When compared with the corresponding data diiodo diiridium(II) complexes [Id&-t-BuS)(CO)L],(Ir-Ir), found in the starting material lb, i.e., 3.216 (2) A and described previously.8 Nevertheless, attempts to prepare 123.20,12these values, together with Ir-S distances and 2b by reaction between [I~I(~-~-BUS)(CO)(P(OM~)~)I~, for Ir-S-Ir and S-Ir-S angles, show that the geometry of the instance, and diazomethane have been unsuccessful. central IrzSzcore of lb is only slightly affected when CHzIz Crystal Structure of the a Isomer of 2b. The crystal structure of the CY isomer of 2b consists of the packing of is added (Figure 2). In agreement with other observations,l the rather large Ir(l)-C(l7)-1r(2) angle of 98.7 (3)O well-separated dinuclear molecules. Figure 1shows a view of the molecule with the atom numbering scheme. Bond distances are given in Table I11 and bond angles in Table (12) Bonnet, J.-J.;Thorez, A.; Maisonnat, A.; Galy, J.; Poilblanc, R. J.Am. Chem. SOC. 1979,101,5940-5948. IV.

Organometallics, Vol. 4, No. 4, 1985 777

Addition of Dihalomethane to Dinuclear Iridium Complexes

R

3 216

T

2.1)

3 198

t

b

4

. i.

2 958

ri C

Figure 2. Schemes of the MzS2and MzSzCcores (M = Ir or Fe) in compounds [I~(~~-BUS)(CO)(P(OM~)~)]~, l b (from ref 12), [I~I(~~-~-BUS)(CO)(P(OM~)~)]~[~-CH~], 2b, and [Fe(r-S-Me)(CO),],[~-C(F)(CF,)](fromref 13). Table V. Infrared Spectran for Complexes 2-6 compd isomer u(CO), cm-I 2111 vs, 2102 s, 2062 vs 2a 2b a 2048 sh, 2038 vs 2b p 2040 vs, 2030 sh 2c oi 2030 sh, 2016 vs 2d a 2018 vs, 2020 sh, 2016 vs, 2028 s 2e a 2028 vs, 2020sh 2e p 2027 sh, 2019 vs 2f a 2030 sh, 2018 vs 3a 2130 s, 2115 s, 2084 vs 4a 2143 s, 2132, 2098 vs 4b 2069 br 4c 2034 br 5a 5b

6a

6b 6b'

6c

2115 s, 2105 s, 2067 s 2115 s, 2070 vs, 2055 s 2104 vs, 2093 s, 2049 vs 2112 vs, 2080 vs, 2065 vs 2069 vs, 2059 sh 2081 s, 2041 vs br, 2016 sh

..

2.41 2f) m Figure 3. 250-MHz 'H NMR spectra (CD2C12)of the a isomer of 2b in the bridging methylene region: (a) at 298 K; (b) at 213 K; (b') 1H(31PJ at 213 K.

Scheme I1 Isomer n

A :, nti trans-anti

Isomer

1,aM-S""

A :,

H H ln"s-a"ll

p P: PlOMDl, t -Bu

d', nn CIS

Hb

- anti

d ':

n. nb CIS-

sin

spectra of the a! isomer of 2b are temperature dependent. In the slow-exchange region, i.e., at 213 K, these spectra a Run in CH,Cl,; s = strong, vs = very strong, sh = are in agreement with the trans-anti conformation obshoulder, br = broad. a and p refer to the two isomeric served in the solid state. The IH NMR spectrum which forms discussed in the text. exhibits two singlets of equal intensity at 1.63 and 1.42 is consistent with the methylene group bridging two nonppm reveals nonequivalent tert-butyl groups consistent bonded iridium atoms and compares well (Figure 2) with with their mutual anti disposition. As expected, the 31P(1HJ that found in the case of the isoelectronic and isostructural spectrum which exhibits two doublets of equal intensity diiron(I1) neutral complex [F~(CO),(K-SM~)]~[P-C(F)-at 65.24 and 63.34 ppm, with doublet spacings of 4.4 Hz, (CF,)], i.e., 93.4" (d(Fe-Fe) = 2.958 (1)A).', reveals nonequivalent and mutually coupled phosphorus Molecular S t r u c t u r e of Complexes 2. IR data of nuclei for the phosphite ligands. On the 'H NMR speccomplexes 2a-f are presented in Table V. Addition of trum, the phosphite protons appear as two doublets of CHzIzor CHzBrzto complexes 1 is accompanied by a shift equal intensity at 3.81 and 3.82 ppm with J p H coupling of of ca. 60-80 cm-' of the u(C0) bands toward higher fre11.3 Hz in both cases. By decoupling the phosphorus quencies, as expected, in fact, for two-electron oxidative nuclei, the methylene resonances appear at 2.47 and 2.33 addition processes on each iridium(1) centers. ppm, as a typical AB patiern (Figure 3b') with a ca. 4.2 lH and 31PNMR characteristics of complexes 2 are Hz coupling between the geminal protons. Further collected in Table VI and VII. The 'H and NMR splitting occurs due to P-H couplings, and the spectrum shown in Figure 3b is interpreted as a poorly resolved AB part of an ABXY spin system, in the first-order approx(13) Bonnet, J.-J.;Mathieu, R.;Poilblanc, R.;b r a , J. A. J.Am. Chem. imation,14with one of the P-H couplings for each methSOC. 1979,101,14a1-1496.

~

778 Organometallics, Vol. 4, No. 4, 1985

El Amane et al.

Table VI. 'H NMRa Data for Complexes 2 isocompd mer 2a 2a 2b 2b

6 ( P -CH,)

T, K

6(PR,)

6 ( p -S-t-Bu)

298 253

1 69 (s, br) 11.59 1.79 (s) (s)

298

3.87 (d, 'JPH= 3.81 (d, 'JPH= 3.82 (d, ' J ~ H = 3.86 ( d , 'JPH=

298 cy

2b

213

{

11.5) 11.3) 11.3) 11.0)

2b

p

213

3.80 ( d , 'JPH= 11.0)

2c

ab

298

7.42(m) 7.76 (m)

2c 2d

ab

ab

203 298

2e 2e 2f

298 298 a b 2 298

ab

Ob

1.61 (br) 1.63 ( S ) 1.42 ( S ) 1.69 ( S ) 1.56 (t, 'JPH = 0 . 7 ) 1.61 i1.48 1.39 (s)

ti(Me) 2 . 6 0 ( d , "p.3

2.49 (s br)

i;::;

AB AA'XX' ABXY ABX,

AA'XX

{

1

'JHH=

2.50 ( 3 J p=~ 5.2) 2.47 ( 'JpH = 7.7) 2.33 ( 3JPH = 6.0) 2.60 ('JPH= o.8) 2.49 ('JpH = 7.6)

{ ;:!; ('JPH

= 7.6) 1.34 ( 'JPH= 7.0)

1.27 (vbr) 1.55 (s) '

d

AA'XX

1.35 ( 'JPH= 7.0)

1.62 ( S )

AA'XX'

2.21 ('JPH = 8.0) 2.46c

5.6

' J H H= 4.2 2JHH

= 4.2

'JHH=4.2

= 11.0)

1.89 (d, 'JPH= 10.6) 1.78 (d, 'JPH= 11.0) 7.39 (m), 7 . 7 6 ( m )

1 1.68 1.57 (s) (s)

1.42 (s)

Run in CD,Cl, at 250 MHz unless otherwise indicated; 6 and J (Hz); s = singlet, d = doublet, t = triplet, m = multiplet, Poorly resolved multibr = broad; a and p refer to the two isomeric forms discussed in the text. Recorded at 90 MHz. plet. Hidden by the broad tert-butyl singlet. a

Table VII. 31P{1H}aand I3Cb NMR Data for Complexes 2 and 6 c compd 2a 2b 2b

isomer

T, K 298 298 213

2b 2b 2c 2c

298 213 298 193

2f 6a 6b'

298 298 298

6 ( 3lP)

62.40 ( s ) 6;53;;p (4Jpp = 4 . 4 )

1

62.15 (s) 64.01 (s) -7.91 ( s ) 1.25 (br) -13.16(br) -10.33 (s) -0.4 (s)

6b 6c

~(P-CH,) -34.76 ( t ) -28.87 (t)

151 149

-29.56 ( t )

147

-16.20 (t)

147

-46.07 ( t ) d -48.74 ( t ) d

'Jcp=

(14) The chemical shift differences bAB and bXy, 35 and 70 Hz,respectively, may be considered aa large compared to coupling constants JARand JXV,4.2 and 4.4 Hz,respectively, so that the first-order approximation is valid.16 (15) Abraham, R.J.;Bematein. H.J. Can. J. Chem. 1961.39.216-230. (16) A Karplus-type dependence of the 8 J p - ~on - ~ the torsion angle is mumed,which is similar to that invoked" for the 3 J p t - p ~in- ~the case of heterodinuclear platinum-palladium complexes containing the bis(dipheny1phosphino)methanebridging ligand. (17) McEwan, D. M.; Pringle, P. G.; Shaw, B. L. J. Chem. Soc., Chem. Commun. 1982, 859-861.

'Jcp=

Hz

7.3 10.5

-66.72d

a At 36.4 MI :. Run in CDCl,; s = singlet, d = doublet, t = triplet, br = broad. At 62.9 M L two isomeric forms discussed in the text. l3CPH }. e See Figure 5.

ylene proton, Ha and Hb, weaker than 1 Hz. We assign these weak couplings to 3J~,pl and 3JH& (Scheme 11)and the couplings of 7.7 and 6.0 Hz to VHaP, and 3JHpl.The relative disposition of Ha,C, Ir2,and P2atoms (the torsion angle Ha-C-Ir2-P2 is 157') might be expected to give larger 3JHp coupling than the relative disposition of Hb, C, Ir2, and P2 atoms (the torison angle Hb-C-Ir2-P2 is 79').16 Upon raising the temperature from 213 to 298 K, the phosphorus ligands become equivalent, as indicated by the coalescence of their 31P(1H)and 'H signals into a single singlet at 62.4 ppm and a single doublet at 3.88 ppm, respectively. Similarly, the tert-butyl groups become equivalent: their singlets coalesce into a single broad singlet at 1.61 ppm. The A and B parts of the ABXY spin

lJCH,

cy

and p refer to the

system for the methylene protons coalesce into a virtual doublet (Figure 3a) interpreted as the envelope of the A part of an AA'XX' spin system in which the X nuclei are mutually weakly coupled. This fluxional behavior of the a isomer of 2b on the NMR time scale may be interpreted in terms of a syn-anti dynamic equilibrium due to an intramolecular endo-exo exchange of the alkylthiolato groups currently observed, for example, in isoelectronic diiron(I1) complexes, [RSFe(CO)(C$15)]21*This process is schematically shown on Scheme 11. The @ isomer of 2b exhibits only one singlet at 62.15 ppm, at 298 K as at 213 K, in the 31P{1HJNMR spectra. In the lH NMR spectra, it exhibits one doublet at 3.80 ppm for the phosphite protons, at 298 K as at 213 K, and, more significantly, one singlet at 1.69 ppm and one triplet at 1.56 ppm (with triplet spacings of 0.7 Hz) of equal intensities for the tert-butyl protons. A relative cis disposition of both carbonyl groups and of both phosphite ligands is then necessarily required for this isomer in which the tert-butyl group resonating at higher chemical shift (18) Dekker, M.;Knox,G. R.;Robertson, C. G. J . Organomet. Chem.

1969,18, 161-167.

Organometallics, Vol. 4, No. 4, 1985 779

Addition of Dihalomethane to Dinuclear Iridium Complexes

Scheme I11 1.

1-Bu

\ d

I

d:

d :,

H H

H H

2:L7

2.3i

in

pp~

is coupled to two equivalent phosphorus nuclei. The bridging methylene proton signal is temperature dependent, as shown in Figure 4. At 298 K, by decoupling the phosphorus nuclei, the methylene resonances appear at 2.60 and 2.49 ppm, as a typical AB pattern (Figure 4a') with a ca. 4.2 Hz coupling between the geminal protons. Further splittings occur due to PH couplings, and the 12-line pattern shown in Figure 4a is interpreted as the fully resolved AB part of an ABX, spin system. The proton resonating at higher chemical shift is weakly coupled (0.8 Hz) to two equivalent phosphorus nuclei whereas the other one is more strongly coupled (7.6 Hz) to two equivalent phosphorus nuceli. We assign the weakly coupled proton, resonating at 2.60 ppm, as Hb and the more strongly coupled proton, resonating at 2.49 ppm, as Ha (see Scheme 11) from consideration of relative values of Ha-C-Ir-P and Hb-C-Ir-P torsion angles, as discussed above. A t 213 K, the spectrum exhibits essentially similar resonance patterns as at 298 K, which may be similarly interpreted as the AB part of an ABXz spin system as expected for a cis isomer in which the methylene protons remain intrinsically nonequivalent whatever the relative disposition of the tert-butyl groups. However, the chemical shift difference between each methylene proton is larger as shown in Figure 4b,b'. From 0.11 ppm at 298 K, this difference is 0.33 ppm at 213 K. The modification of the

1'

H H 5 a,b

N

2.b

L a-c

H H 3N .

I-BU

Figure 4. 250-MH 'H NMR spectra (CD2C12)of a mixture of the CY and p isomers of 2b ([a]:[P] = 1:2)in the bridging methylene region: (a) at 298 K; (a') 1H(31P)at 298 K; (b) at 213 K (b') 31P(1HJ at 213 K.

124

6a-c N

relative disposition of the tert-butyl groups of the thiolato bridging ligands is assumed again to be responsible for chemical shift variations. To sum up, the adduct 2b exhibits stereoisomerism at the metal atom as well as at the bridging groups. If no dynamic interconversion was detected between cis (a)and trans (p) stereoisomericforms, the syn-anti interconversion is a fast process at the NMR time scale. Similar basic structures containing bridging methylene entities and iodide ligands in apical positions, one on each iridium atom, were found from spectroscopic measurements for the other CH212adducts 2, and nonrigidity of the tert-butyl groups of the thiolato bridging ligands was observed in each case. Thus, the Occurrence of three v(C0) modes in the IR spectrum of 2a obviously indicates a retention of the CZusymmetry of the starting material la when CH212is added. Moreover, the 'H NMR spectrum of this adduct, which is temperature-dependent, exhibits in the slow-exchangeregion two singlets of equal intensities for the tert-butyl groups at 1.79 and 1.59 ppm, consistent with an anti relative disposition of these groups. Consequently, the methylene proton resonances appear at 2.57 and 2.45 ppm as a typical AB pattern with a JHH of 5.6 Hz. Upon raising the temperature, the tert-butyl groups as well as the methylene protons become equivalent and their resonance signals coalesce into broad singlets. In cases 2c and 2d, only one isomer was formed by oxidative addition of CHzXzto the corresponding materials IC and Id. As in the a isomer of 2b, a relative trans disposition of both carbonyl groups and of both phosphine ligands was deduced from NMR data. As shown in Table VII, the 13C chemical shifts of the p-CH, groups of the CHzIzadducts 2 lie in an unexpected range, from -15 to -35 ppm, if compared with values observed for other complexes in which the methylene ligand bridged two nonbonded metal at0ms.l These signals appear as triplets on the I3C NMR spectrum, with 2JcH coupling constants of about 150 Hz, whereas no 2Jcpwas detected for these complexes, probably owing to the relative cis disposition of phosphine ligands and of the bridging methylene group. Halide Abstraction Reaction of Complexes 2 by Silver(1) Salts. Complexes 2 are easily dehalogenated in dichloromethane at room temperature, using stoichiometric quantities of silver(1) salts (perchlorate or hexafluorophosphate) leading to dicationic species 4 (Scheme 111). Monitored by IR in the case of 2a, a monocationic intermediate, 3a, was detected in solution indicating that the reaction proceeds by successive abstraction of each iodide ligand. The dicationic compounds 4 which contain five-coordinated iridium(II1) centers are opened to nu-

El Amane et al.

780 Organometallics, Vol. 4, No. 4, 1985

95

93

‘

6

1

2

1

60 1

and 6c as shown by their IR spectra in the v(C0) region. The added phosphines in 6a occupy equivalent positions, as expected. The 31P(1HJ NMR spectrum of 6b’ (6b’ results from the iodide abstraction reaction of a a isomer of 2b followed by the addition of 2 equivalents of P(OMe)3)exhibits two identical patterns, each pattern containing five pairs of symmetrical lines respectively centered at 93.72 and 61.26 ppm (Figure 5). This is characteristic of an AA’XX’ spin system, and it can be analyzed in terms of the parameters K , L, M , and N defined as K = JAA’+ J”, L = JAx- JAxl, M = JAA,,- Jxx,,and N = JAx + JAxt.This is fully consistent with the proposed structure which contains one pair of equivalent axial and one pair of equivalent equatorial phosphite ligands. A mutual trans disposition of both equatorial phosphites and of both carbonyl ligands is deduced from the equivalence of the tert-butyl groups of the thiolato bridging ligands. 2’

Figure 5. 36.4-MHz 31P(1H} NMR spectrum (CD2C12)of 6b’.

cleophilic attack, and complexes 6a-c are quantitatively obtained by addition of tertiary phosphine or carbon monoxide to dichloromethane solutions of the dicationic species 4. Moreover, when the halide abstraction reaction is accompanied by the addition of tertiary phosphine or carried out under carbon monoxide atmosphere, complexes 6a,b are obtained quantitatively, whereas monocationic intermediates 5a,b are detected in solution by IR. Complexes 6a-c form air-stable, pale yellow solids which dissolve in dichloromethane, methanol, or tetrahydrofuran but which are insoluble in toluene or petroleum ether. Conductimetric measurements indicate that these complexes are 1:2 electrolytes in methanol solutions. Spectroscopic studies indicate that the geometry of these complexes can be simply deduced from the geometry of the starting material 2 by the substitution of iodide ligands for the entering nucleophiles. As an example, the iodide abstraction reaction of complex 2a leading to complex 4a is accompanied by a shift of c a 32 cm-l of the three v(C0) bands toward higher frequencies, and the subsequent addition of triphenylphosphine, leading to 6a, is accompanied by a shift of ca. 40 cm-l of these bands toward lower frequencies. These observations are indicative of a retention of the relative disposition of the four carbonyl groups in the molecules during the reactions, according to a C2” symmetry. Moreover, the replacement of both iodides ligands by triphenylphosphine in 2a and by carbon monoxide in 2c leads significantly to two distinct dications 6a

H- H P P(OMei,

6,“

The 13C resonances of the p C H 2 group of 6a, 6b, 6b’, and 6c are shifted considerably toward higher field and lie in a quite unexpected range, i.e., ca. -40 to -65 ppm. The 13C(lHJNMR resonances of 6a and 6b’ appear as triplets with 2Jcp coupling constants of 7.3 and 10.5 Hz, respectively.

Acknowledgment. We wish to thank G. Commenges for experimental assistance in NMR and the CNRS for financial support. Registry No. la, 63312-27-6; lb, 63292-76-2;lo, 63264-36-8; Id, 94890-43-4; le, 63292-79-5;2a, 94890-44-5;a-2b, 94890-45-6; p2b, 94942-80-0; 20,94890-46-7;2a, 94890-47-8; d e , 94890-48-9; &2e, 94942-81-1; 2f, 94904-36-6; 3a, 94890-50-3; 4a, 94890-52-5; 4b,94890-54-7;4c, 94890-56-9; 5a, 94890-58-1; 5b, 94890-60-5; 6a, 94890-62-7; 6b, 94890-64-9;6b’, 94890-66-1;6c, 94943-28-9;CH&, 75-11-6;CH&, 74-95-3; [I~I(~-~-BuS)(CO)(P(OM~)~)]~, 7414413-1; diazomethane, 334-88-3. Supplementary Material Available: Tables of observed and calculated structure factors for 2b, final anisotropic thermal parameters for non-hydrogen atoms, hydrogen positional and thermal parameters, least-squares plane equations (18 pages). Ordering information is given on any current masthead page.